This invention relates generally to the laser art and more particularly to means for and a method of performing logical operations using two temporally and spatially modulated laser beams, with the result of the logical operation appearing as spatial and temporal modulation on one of the two laser beams. Such logical operations include the AND, OR, and NOT operations, as are performed by any electronic computer.
It is well known that two laser beams can interact with each other in a medium having a third-order nonlinear optical susceptibility. This interaction will occur if the frequencies of the two beams are separated by the so-called Stokes frequency shift which depends on the third order nonlinear optical susceptibility. This interaction may transfer energy and phase from a beam of one optical frequency to another beam of a second optical frequency, such as occurs with stimulated Brillouin or stimulated Raman scattering. The former laser beam is referred to as the pump laser beam, and the latter is referred to as the Stokes laser beam. For a further discussion of Brillouin scattering reference is made to the discussion of Brillouin scattering by B. Zeldovich et al, JETP Lett. 15, 109 (1972) and for a further discussion of Raman scattering reference is made to the discussion of Raman scattering by E. Garmire et al, Phys. Rev. Lett. 11, 160 (1963), both of which are incorporated herein as if set out at length.
It is well known that four-wave mixing is such an interaction, and that the four-wave mixing process has been used in both gases and photorefractive media to combine information. Four-wave mixing has been applied to matrix-vector multiplication and correlations. Such matrixvector calculations consist of multiplying and adding together two sets of numbers. For a further discussion of four-wave mixing see "Image Phase Compensation And Real-Time Holography By Four-Wave Mixing In Optical Fibers", by A. Yariv et al, Appl. Phys. Lett. 32, 635 (1978); for a further discussion of matrix-vector multiplication and correlation see "Optical Matrix-Vector Multiplication Through Four-Wave Mixing in Photorefractive Media", by P. Yeh et al, Opt. Lett. 12, 138 (1987). Previous work has used four-wave mixing in which the data located at separate spatial locations is combined separately and in parallel. See the aforementioned Yariv article as well as "Spatial Convolution And Correlation Of Optical Fields Via Degenerate Four-Wave Mixing", Opt. Lett. 3, 7 (1978). These approaches require significant power and have undesirable cross-talk between data at different points, i.e., between different spatial modes.
It is also well known that in an appropriate geometry and an appropriate medium the so-called `mode` approximation holds. In this regime, different spatial frequencies of two beams transfer energy only. That is, under suitable conditions the phases of differing spatial modes are not transferred between each other, and the growth of a spatial mode is determined only by the pump and Stokes light in the same mode, the overall intensity, and the overall pump-Stokes correlation. This mode approximation is well known in interactions which start from noise at the Stokes frequency. Such interactions include the well-known non-linear optical phase conjugation effect. For a further discussion of the mode approximation see "Calculations of The Accuracy of Wavefront Reversal Utilizing Pump Radiation With One-Dimensional Transverse Modulation", by B. Ya. Zeldovich et al, Sov. J. Quant. Electron, 11, 186 (1981).